System and method for manufacturing magnetic resonance imaging gradient coil assemblies

ABSTRACT

The embodiments disclosed herein relate generally to magnetic resonance imaging systems and, more specifically, to the manufacturing of a gradient coil assembly for magnetic resonance imaging (MRI) systems. For example, in one embodiment, a method of manufacturing a gradient coil assembly for a magnetic resonance imaging system includes depositing a first layer comprising a base material onto a surface to form a substrate and depositing a second layer onto the first layer. The second layer may enable bonding between a conductor material and the substrate. The method also includes depositing a third layer onto the second layer using a consolidation process. The consolidation process uses the conductor material to form at least a portion of a gradient coil.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. patent application Ser. No.13/859,586, filed on Apr. 9, 2013, the disclosure of which isincorporated herein by reference in its entirety.

BACKGROUND

This section is intended to introduce the reader to various aspects ofart that may be related to various aspects of the present disclosure,which are described and/or claimed below. This discussion is believed tobe helpful in providing the reader with background information tofacilitate a better understanding of the various aspects of the presentdisclosure. Accordingly, it should be understood that these statementsare to be read in this light, and not as admissions of prior art.

Magnetic Resonance Imaging (MRI) systems enable imaging based on aprimary magnetic field, a radio frequency (RF) pulse, and time-varyingmagnetic gradient fields that interact with specific nuclear componentsin an object, such as hydrogen nuclei in water molecules. The magneticmoments of such nuclei may generally align with the primary magneticfield, but subsequently precess about the bulk magnetic field directionat a characteristic frequency known as the Larmor frequency. An RF pulseat or near the Larmor frequency of such nuclei may cause their magneticmoments to be rotated. When the RF pulse has ended, the magnetic momentsrelax and generally align with the primary magnetic field, emitting adetectable signal.

Some of the magnetic gradient fields in MRI are produced by a series ofgradient coils. In particular, the gradient coils create magnetic fieldsof varying strength along various imaging planes to produce a gradientalong each plane. Nuclei of interest (e.g., hydrogen) align their spinsaccording to the gradients. This results in spatial encoding, wherespatial information about the location of the excited hydrogen nucleican be obtained during acquisitions. Strong amplifiers power thegradient coils, allowing them to rapidly and precisely adjust themagnetic field gradients.

Generally, gradient coils for conventional cylindrical whole bodymagnetic resonance imaging (MRI) systems are manufactured by layingmachined or wound electrical conductor material that has been rolledinto a cylindrical shape onto a cylindrical former. Planar and othernon-right circular cylindrical geometries for the gradient coils arealso used for MRI. The teachings in this application herein do notpreclude its use in non-right circular cylindrical geometries and are infact applicable to other geometries. Moreover, various other layersincluding spacers, dielectric insulators, cooling features, passive shimbars, resistive shim assemblies, and RF shield are laid onto thecylindrical former to complete a gradient coil assembly. The performanceof the gradient coils is dependent, at least in part, on the precisealignment of the layers before being fixed or bound to the cylindricalformer. In addition, the manner in which the gradient coils are formedmay affect their durability. For example, the durability of the gradientcoils may decrease due to stress resulting from winding or otherwisebending the coils to a desired shape. Furthermore, additional gradientcoil features (e.g. soldering pads, connecting leads, jumpers and barbs)are brazed onto the MRI gradient boards, which can introduce weak pointsinto the coil assembly. Unfortunately, many of the above processes maybe performed by hand, which can introduce manufacturer error anduncertainty into the overall manufacturing process.

BRIEF DESCRIPTION

In one embodiment, a method of manufacturing a gradient coil assemblyfor a magnetic resonance imaging system includes depositing a firstlayer including a base material onto a surface to form a substrate anddepositing a second layer onto the first layer. The second layer mayenable bonding between a conductor material and the substrate. Themethod also includes depositing a third layer onto the second layerusing a consolidation process. The consolidation process uses theconductor material to form at least a portion of a gradient coil.

In another embodiment, a system, includes an additive manufacturingsystem including a plurality of configurable elements that may deposit aplurality of materials to form a gradient coil assembly, a platformincluding a mandrel that may support the plurality of materials as theyare deposited, a control system communicatively coupled to the additivemanufacturing system, the platform, or a combination thereof. Thecontrol system may control the additive manufacturing system, theplatform, or the combination thereof, such that the system produces aninductor having one or more internal fluid paths, and a qualityinspection module that may provide feedback to the control system. Thefeedback includes information about the inductor.

In a further embodiment, a system includes a controller that may operatean additive manufacturing system to produce an inductor and an inlinequality inspection module communicatively coupled to the controller. Theinline quality inspection module may inspect the inductor and providefeedback relating to one or more inductor parameters to the controller.The controller may receive the one or more inductor parameters andadjust an operational parameter of the additive manufacturing systembased on the received one or more inductor parameters.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features, aspects, and advantages of the presentinvention will become better understood when the following detaileddescription is read with reference to the accompanying drawings in whichlike characters represent like parts throughout the drawings, wherein:

FIG. 1 is a diagram of an embodiment of a MRI system utilizing one ormore gradient coils;

FIG. 2 is a process-flow diagram of an embodiment of a method formanufacturing MRI gradient coil assemblies having cooling channels;

FIG. 3 is a cross-sectional view of an embodiment of a gradient coilassembly resulting from steps of the method of FIG. 2;

FIG. 4 is a cross-sectional view of an embodiment of a gradient coilassembly having a bonding layer deposited according to the method ofFIG. 2;

FIG. 5 is a cross-sectional view of an embodiment of a gradient coilboard having MRI gradient coils with cooling channels depositedaccording to the method of FIG. 2;

FIG. 6; is a cross-sectional view of an embodiment of an MRI gradientcoil board having a spacer deposited according to the method of FIG. 2;

FIG. 7 is a cross-sectional view of an MRI gradient coil board resultingfrom various steps of the method of FIG. 2;

FIG. 8 is a process-flow diagram of an embodiment of a method formanufacturing the MRI gradient coils with cooling channels depicted inFIG. 5;

FIG. 9; is a diagrammatical illustration of an embodiment of an MRIgradient coil resulting from various steps of the method of FIG. 8; and

FIG. 10 is a diagrammatical illustration of an embodiment of a systemused to manufacture MRI gradient coil assemblies.

DETAILED DESCRIPTION

One or more specific embodiments will be described below. In an effortto provide a concise description of these embodiments, all features ofan actual implementation may not be described in the specification. Itshould be appreciated that in the development of any such actualimplementation, as in any engineering or design project, numerousimplementation-specific decisions must be made to achieve thedevelopers' specific goals, such as compliance with system-related andbusiness-related constraints, which may vary from one implementation toanother. Moreover, it should be appreciated that such a developmenteffort might be complex and time consuming, but would nevertheless be aroutine undertaking of design, fabrication, and manufacture for those ofordinary skill having the benefit of this disclosure.

When introducing elements of various embodiments of the presentinvention, the articles “a,” “an,” “the,” and “said” are intended tomean that there are one or more of the elements. The terms “comprising,”“including,” and “having” are intended to be inclusive and mean thatthere may be additional elements other than the listed elements.Furthermore, any numerical examples in the following discussion areintended to be non-limiting, and thus additional numerical values,ranges, and percentages are within the scope of the disclosedembodiments.

As noted above, certain processes used to manufacture gradient coilassemblies can be costly, can introduce structural weaknesses into theassemblies, and may result in certain manufacturing defects.Accordingly, it may be desirable to manufacture gradient coil assembliesautomatically and in a manner that results in less susceptibility tomanufacturing defects and structural instabilities. The presentdisclosure provides embodiments directed toward manufacturing gradientcoil assemblies using one or more additive manufacturing techniques.

For example, the present disclosure provides embodiments formanufacturing gradient coils using electron beam deposition, laserpowder deposition, or ultrasonic consolidation. One or more additionaladditive manufacturing techniques may be used to combine the gradientcoils with other gradient coil assembly features, such as spacers,windings, dielectric insulators, and so on. Indeed, in one embodiment, agradient assembly may be automatically built using an automated gradientcoil assembly manufacturing system, which may result in reducedmanufacturing time while enhancing manufacturing precision, processcontrol, and reliability compared to more traditional manufacturingapproaches, such as manual winding and assembly.

Again, the gradient coil assemblies disclosed herein may be utilized inany magnetic resonance system, such as those commonly used in medicalimaging. Turning now to the drawings, and referring first to FIG. 1, anembodiment of such an MRI system 10 is illustrated diagrammatically asincluding a scanner 12, scanner control circuitry 14, and system controlcircuitry 16. While the MRI system 10 may include any suitable MRIscanner or detector, in the illustrated embodiment the system includes afull body scanner having a table 20 positioned to place a patient 22 ina desired position for scanning.

The scanner 12 may include a series of associated coils for producingcontrolled magnetic fields, for generating radio frequency (RF)excitation pulses, and for detecting emissions from gyromagneticmaterial within the patient in response to such pulses. In thediagrammatical view of FIG. 1, a main magnet 24 is provided forgenerating a primary magnetic field. A series of gradient coils 26, 28and 30 are grouped in one or more gradient coil assemblies forgenerating controlled magnetic gradient fields during examinationsequences. An RF coil 32 is provided for generating RF pulses forexciting the gyromagnetic material. Power may be supplied to the scanner12 in any appropriate manner, as indicated generally at referencenumeral 34. In the embodiment illustrated in FIG. 1, the RF coil 32 mayalso serve as a receiving coil. Thus, the RF coil 32 may be coupled withdriving and receiving circuitry in passive and active modes forreceiving emissions from the gyromagnetic material and for applying RFexcitation pulses, respectively. Alternatively, various configurationsof receiving coils 36 may be provided separate from RF coil 32. Suchcoils may include structures specifically adapted for target anatomies,such as head coil assemblies. Moreover, receiving coils may be providedin any suitable physical configuration, including phased array coils.

In accordance with an embodiment, the gradient coils 26, 28, and 30 mayeach be formed using conductive wires, bars, plates or sheets to form acoil structure, which generates a gradient field upon application ofcontrol pulses. The placement of the gradient coils 26, 28, and 30within the gradient coil assembly may be done in several differentorders and with varying configurations, and the scanner 12 may furtherinclude complementary gradient coils to shield the gradient coils 26,28, and 30. In some embodiments, the gradient coil 26 may be az-gradient positioned at an outermost location compared to the gradientcoils 28 and 30. The gradient coils 28 and 30 may be x-axis and y-axiscoils, respectively.

The gradient coils 26, 28, and 30 of the scanner 12 may be controlled byexternal circuitry to generate desired fields and pulses, and to readsignals from the gyromagnetic material in a controlled manner. Thegradient coils 26, 28, and 30 may also serve to generate preciselycontrolled magnetic fields, the strength of which vary over a predefinedfield of view, typically with positive and negative polarity. When eachgradient coil 26, 28, or 30 is energized with known electric current,the resulting magnetic field gradient is superimposed over the primaryfield and produces a desirably linear variation in the axial componentof the magnetic field strength across the field of view. The field mayvary linearly in one direction, but may be homogenous in the other two.The three gradient coils 26, 28, and 30 may have mutually orthogonalaxes for the direction of their variation, enabling a linear fieldgradient to be imposed in an arbitrary direction with an appropriatecombination of the three gradient coils 26, 28, and 30.

The pulsed gradient fields may perform various functions integral to theimaging process. Some of these functions are slice selection, frequencyencoding and/or phase encoding. These functions can be applied along thex-, y- and z-axes of the original coordinate system or along other axesdetermined by combinations of pulsed currents applied to the individualfield coils.

The coils of the scanner 12 are controlled by the scanner controlcircuitry 14 to generate the desired magnetic field and radiofrequencypulses. In the embodiment of FIG. 1, the control circuitry 14 thusincludes a control circuit 38 for commanding the pulse sequencesemployed during the examinations, and for processing received signals.The control circuit 38 may include any suitable programmable logicdevice, such as a CPU or digital signal processor of a general purposeor application-specific computer. Further, the control circuit 38 mayinclude memory circuitry 40, such as volatile and/or non-volatile memorydevices for storing physical and logical axis configuration parameters,examination pulse sequence descriptions, acquired image data,programming routines, and so forth, used during the examinationsequences implemented by the scanner 12.

Interface between the control circuit 38 and the coils of the scanner 12may be managed by amplification and control circuitry 42 and bytransmission and receive interface circuitry 44. The amplification andcontrol circuitry 42 includes amplifiers for each gradient field coil26, 28, and 30 to supply drive current in response to control signalsfrom the control circuit 38. The receive interface circuitry 44 includesadditional amplification circuitry for driving the RF coil 32. Moreover,where the RF coil 32 serves both to emit the RF excitation pulses and toreceive MR signals, the receive interface circuitry 44 may include aswitching device for toggling the RF coil between active or transmittingmode, and passive or receiving mode. A power supply, denoted generallyby reference numeral 34 in FIG. 1, is provided for energizing theprimary magnet 24. Finally, the scanner control circuitry 14 includesinterface components 46 for exchanging configuration and image data withthe system control circuitry 16.

The system control circuitry 16 may include a wide range of devices forfacilitating interface between an operator or radiologist and thescanner 12 via the scanner control circuitry 14. In the illustratedembodiment, for example, an operator workstation 48 is provided in theform of a computer workstation employing a general purpose orapplication-specific computer. The operator workstation 48 alsotypically includes memory circuitry for storing examination pulsesequence descriptions, examination protocols, user and patient data,image data, both raw and processed, and so forth. The operatorworkstation 48 may further include various interface and peripheraldrivers for receiving and exchanging data with local and remote devices.In the illustrated embodiment, such devices include a monitor 50, aconventional computer keyboard 52, and an alternative input device suchas a mouse 54. A printer 56 is provided for generating hard copy outputof documents and images reconstructed from the acquired data. Inaddition, the system 10 may include various local and remote imageaccess and examination control devices, represented generally byreference numeral 58 in FIG. 1. Such devices may include picturearchiving and communication systems, teleradiology systems, and thelike.

As noted above, the present disclosure provides, among other things,techniques that may be used to construct gradient coil assemblies, suchas a gradient coil assembly including gradient coils 26, 28, and 30, ina manner that enables the gradient coil assemblies to be built in anautomated system. The automated system may construct the gradient coilassemblies layer by layer, while also constructing the coils in a widevariety of geometries. One such approach is depicted in FIG. 2, whichillustrates an embodiment of a method 60 to construct the gradient coilassembly having coils 26, 28, and 30 used in the MRI system 10 ofFIG. 1. In addition, to facilitate discussion of aspects of the method60, reference is made to corresponding structures resulting from theacts of the method 60 in FIGS. 3-9. It should be noted that the method60 may be performed automatically, such as by an automated system asdescribed in detail with respect to FIG. 10, by a user, or both. Indeed,any one or a combination of the method steps described herein may beperformed by such a system, which may include one or more tangible,non-transitory, machine-readable media storing one or more sets ofinstructions, and one or more processing devices configured to executethe one or more sets of instructions, where the one or more sets ofinstructions, when executed, perform the automated steps describedherein.

The method 60 includes providing a former, a substrate material, whichmay include a fiberglass reinforced polymer or any other non-conductivedurable materials suitable for supporting and/or housing a gradient coilassembly, and a conductor (e.g., coil) material, such as aluminum,copper, their respective alloys, or any other suitable conductivematerial that may be used to form a gradient coil (block 62). The method60 also includes depositing the substrate material on the former/mandrel(block 64) to produce a base layer to form a flat or cylindricalgradient coil board.

One embodiment of a structure resulting from the acts of block 64 isdecpited in FIG. 3. In particular, FIG. 3 illustrates a cross-sectionalview of an embodiment of a gradient board 66 having a base layer 68(e.g., a substrate layer) deposited onto a mandrel 70 and having adesired thickness T₁. As discussed above, the composite or base materialmay include fiber reinforced polymers such as, but not limited to,epoxy, vinylester, and polyester thermosets, phenyl formaldehyde resins,polyurethanes, furans, polyimides, or any other suitable polymer havingfibers including, but not limited to, glass, aramid, carbon, boron, orany combination thereof. It should be appreciated that the fibers may beimpregnated, pre-impregnated, or post impregnated with the desiredpolymer and/or resin. Any suitable composite winding process (e.g.,filament winding) may be used to deposit the composite material onto themandrel 70 to yield the gradient coil board 66. The fibers in each ofthe layers of former material in the base layer 68 may be oriented inthe same direction or may be oriented in different directions. That is,each layer may have a fiber orientation different from the previouslayer. The base layer 68 may be cured using physical or chemicalprocesses known to those skilled in the art once the desired thicknessT₁ has been achieved. In one embodiment, the base layer 68 may be cured(e.g., in an oven) after deposition of each layer of base material inthe base layer 68. In other embodiments the base layer 68 may be curedafter several layers of base material have been deposited in the baselayer 68. For example, the base layer 68 may be cured after 10%, 25%,75%, and/or 100% of the thickness T₁ has been achieved. In otherembodiments, the base layer 68 may be cured after completion of thegradient board assembly.

Returning to the method 60 in FIG. 2, following deposition of the baselayer 68, a conductive bonding layer is deposited onto the base layer 68(block 72). In accordance with block 72, as depicted in FIG. 4, abonding layer 74 is deposited onto the base layer 68 of the gradientboard 66. The bonding layer 74 may include a radio frequency (RF) shieldmaterial such as, but not limited to, copper, nickel, aluminum, andtheir alloys, metal clad materials, metal inks or a combination thereof.Furthermore, the bonding layer may have a thickness T₂ that may besimilar or different than the thickness T₁ of the base layer 68 and maybe of any design. For example, the bonding layer 74 design may include aconductive mesh and/or sheet, such that high frequency RF signals can becontained within its boundaries. In other words, in one embodiment, thebonding layer 74 may be a Faraday shield. Deposition of the bondinglayer 74 may be performed by a cold spraying process (e.g., gas dynamiccold spray) however, any other suitable spray process may be utilized.After deposition of the bonding layer 74, an additional layer of thebase material may be deposited to seal the bonding layer 74 and fill inany voids resulting from the particular bonding layer design.

Turning once again to the method 60 in FIG. 2, following deposition ofthe bonding layer 74, conductor and cooling channel patterns aredeposited (block 76) to form gradient coil geometries (e.g., gradientcoils 26, 28, 30 of FIG. 1) and/or resistive shim coil geometries on thegradient board 66. FIG. 5 is a cross-sectional view of an embodiment ofthe gradient board 66 on the mandrel 70 having the base layer 68, thebonding layer 74, and a gradient coil (or resistive shim coil) layer 78resulting from the performance of the acts of block 76. It should benoted that to facilitate discussion, certain embodiments describedherein are presented in the context of including gradient coils (e.g.,within the gradient coil layer 78). However, it should also be notedthat any one or a combination of the gradient coil layers (e.g., layer78) disclosed herein may, additionally or alternatively, include one ormore resistive shim coils. Accordingly, while gradient coils may bespecifically referenced below, the incorporation of resistive shim coilsis also presently contemplated.

The conductor material used to produce the gradient or resistive shimcoils may be deposited using various metal deposition methods such as,but not limited to, ultrasonic consolidation, laser sintering, lasercladding, conductive ink printing, and/or electron beam welding to formthe gradient (or resistive shim) coils 26, 28, and 30. In oneembodiment, the gradient coil layer 78 is deposited using ultrasonicconsolidation, as discussed below with respect to FIGS. 8 and 9.Further, the same deposition method can be used to connect the differentsections of the cooling or electrical conductor pattern and provideleads, jumpers, and coolant fittings before, during, or after formingthe gradient coil geometries.

Referring back to the method 60 in FIG. 2, upon completion of thegradient coil layer 78, a dielectric spacer layer is deposited (block80). A cross-sectional view of the gradient board 66 including themandrel 70, the base layer 68, the gradient coil layer 78, the bondinglayer 74, and a dielectric spacer layer 82 deposited according to block80, is illustrated in FIG. 8. As depicted, the dielectric spacer layer82 may provide additional structural support for the board 66, and mayfill voids between portions of the gradient coil layer 78 (e.g., toprovide a substantially flat or continuous surface). Furthermore, thedielectric spacer layer 82 may electrically isolate the gradient coils26, 28, and 30 from external electrical conductors, such as those usedto provide current to the gradient coils 26, 28, and 30, except atcontact points where electrical current is provided to and from thecoils.

Deposition of the dielectric spacer layer 82 may be achieved using anyprocess suitable for depositing dielectric materials. For example, incertain embodiments, the dielectric spacer layer 82 may be depositedusing a printer head or a spray process. The dielectric spacer layer 82may include material having high dielectric (e.g., electricallyinsulative) properties, such as, but not limited to, a ceramic or aceramic/epoxy composite, or any other suitable composite materials.Furthermore, the dielectric spacer layer 82 may include a combination oflayers made using a dielectric material and the base material. In someembodiments, the dielectric spacer layer 82 may be disposed onto thegradient coil layer 78 prior to deposition of subsequent gradient coillayers 78 to prevent shorting between gradient coil layers.

Following deposition of the dielectric spacer layer 82 according toblock 80, the method 60 includes determining (query 84) whether the coilassembly is complete. For example, in embodiments in which the method 60is automated, the control circuitry of the automated system maydetermine whether the coil has the predefined geometries, number ofconductive and/or insulative layers, or the like. For example, in oneembodiment, additional bonding layers 74, gradient coil layers 78, anddielectric spacer layers 82 may be used to complete the gradient coilboard 66. Therefore steps 72, 76, and 80 of the method 60 may berepeated until the system determines that the gradient coil assembly iscompleted. One embodiment of a completed gradient coil assembly 86having a pre-defined number of gradient coil layers 78, bonding layers74, and spacer layers 82 is illustrated as a cross-sectional diagram inFIG. 7. It should be noted that the gradient coil assembly 86 may haveany number of layers, such as 1, 2, 3, 4, 5, or more bonding, gradient,and/or dielectric spacer layers.

In addition to the layers discussed above, the gradient coil assembly 86may have resistive shim assemblies and/or passive shim tooling barsdeposited and distributed between each of the layers. For example, incertain embodiments, one or more resistive shim assemblies each havingone or more resistive shim coils may be interleaved with one or moregradient coil layers according to block 76 of the method 60 (FIG. 2) ina similar manner as described above with respect to the gradient coillayer. Accordingly, after deposition of the dielectric spacer layer 82(e.g., according to block 80 (FIG. 2)) and the bonding layer 74 (e.g.,according to block 72 (FIG. 2)), the resistive shim assemblies havingone or more inductors may be deposited. After deposition of theresistive shim assemblies, the acts according to blocks 72, 76, 80, and84 may be repeated until a predetermined number of gradient coil layersand resistive shim assemblies are incorporated into the gradient coilassembly 86.

In other embodiments, fugitive inks may be deposited inside the bondinglayer 74 to form shim pockets. In certain embodiments, the fugitive inkmay also be used to form hollow conducting channels within the gradientboard. The fugitive ink may be removed via chemical or physical methods(e.g., dissolution, flushing, ejecting, etc.) once the gradient coilassembly 86 is complete, leaving hollow cavities (e.g., shim pockets)within the bonding layer 76. Furthermore, the fugitive ink may beremoved by using warm water to dissolve and flush out the fugitive inkfrom within the bonding layer 74. In other embodiments, an abrasiveslurry (e.g., a sand-water mixture) may be passed through at a pressuresuch that it removes the fugitive ink and smooths out the shim pocketsor any other hollow cavities such as the conducting channels within thegradient coil assembly 86.

Once it is determined, in query 84, that the coil assembly 86 iscomplete, jumpers and cooling connections may be deposited onto thegradient coil assembly 86 (block 88), though it should be appreciatedthat such connections may be deposited during deposition of the gradientcoil layers 78. It should be noted that prior to deposition of thejumpers and/or cooling connections, a layer of base material (e.g.,similar to or the same as the base layer 70) may be deposited. Thejumpers, cooling connections, and other similar connectors may be formedusing the metal deposition techniques discussed above (e.g., ultrasonicconsolidation, laser sintering, laser cladding, electron beam wiredeposition). Accordingly, three-dimensional features such as electricalconnectors, inlet connectors, and outlet connectors may be depositedonto the gradient coil assembly 86 without soldering and/or brazing theconnectors, which may enhance durability.

Because the connectors may be used for coupling to cooling fluidsources, the connectors may include internal fluid paths, which enablethe flow of the coolant into cooling channels 90 of the coils.Furthermore, the connectors may have geometries that are more conducivefor securing with external cooling and/or electrical sources. Forexample, the connectors may have smooth and/or rounded edges, smooththreads, or a combination thereof, such that tube fittings may be usedto secure the tubing from the cooling source to the connectors. As notedabove, upon complete deposition of the jumpers and/or cooling connector(e.g., after all layers of the gradient coil assembly 86 are in place),the gradient coil assembly 86 may be placed in an oven or other suitableheating source to cure any remaining uncured composite material (e.g.,former material).

As set forth above with respect to block 76 of FIG. 2, in certainembodiments, ultrasonic consolidation may be utilized to depositconductive channels for use as gradient coils in the gradient coilassembly 86. FIG. 8 illustrates an embodiment of a method 100 forconstructing the gradient coils 26, 28, and 30 using ultrasonicconsolidation. In addition, to facilitate discussion of aspects of themethod 100, reference is made to corresponding structures resulting fromthe acts of the method 100 in FIG. 9.

The method 100 includes depositing a first plurality of sheets of aconductor material (e.g., the coil material) onto a substrate (e.g., thebase layer or the seed layer), and ultrasonically consolidating thefirst plurality of sheets of the conductor material together to form astructure (block 102). For example, with reference to FIG. 9, theconfiguration resulting from the acts of block 102 are depicted. Movingfrom left to right, the diagram in FIG. 9 illustrates a first pluralityof metal sheets 104 having a desired thickness T₃ deposited onto asubstrate 106 (e.g., the bonding layer 74 in FIG. 4), according to theacts of block 102. The thickness T₃ of the first plurality of metalsheets 104 may be any suitable size, such as between 0.02 and 0.001inches, 0.012 and 0.003 inches, 0.009 and 0.005 inches, or approximately0.006 inches. The metal sheets may include any conductive materialsuitable for ultrasonic consolidation to produce the gradient coils 26,28, and 30. By way of example, such materials may include highlyconductive metals such as 101 OFHC copper, aluminum, and theirrespective alloys, among others. By applying a suitable amount of forceand ultrasonic vibrations (e.g., a frequency of approximately 20 kHz) toeach metal layer, the first plurality of metal sheets 104 areconsolidated to form a first consolidated structure 108 having athickness T₄ of approximately 1 to 10 mm.

Returning to the method 100 of FIG. 8, following consolidation of thefirst plurality of metal sheets, cooling channels are machined into theconsolidated structure (block 110). In accordance with block 110, asdepicted in the middle structure in FIG. 9, a cavity 112 is machinedinto the first consolidated structure 108. The cavity 112 may be used togenerally define the size (e.g., cross-sectional area) of one or moreinternal cooling channels formed into the coil resulting from the method100. Accordingly, the size of the cavity 112 will generally correspondto the size of the cooling channel. While any relative size is presentlycontemplated, by way of non-limiting example, the thickness of thecavity 112 may be at least approximately 10% of the thickness of thefirst consolidated structure 108, such as between approximately 10% and90% of the thickness, between approximately 20% and 80% of thethickness, or between approximately 30% and 60% of the thickness of thefirst consolidated structure 108.

Returning again to the method 100 of FIG. 8, upon machining inaccordance with block 110, the method 100 includes sealing the machinedcooling channels by ultrasonically consolidating a second plurality ofsheets of the conductor material to the first plurality of sheets of theconductor material (block 114). Referring again to FIG. 9, referring tothe structure at the right, a second plurality of metal sheets 116 areconsolidated to the first plurality of metal sheets 108 to form a secondconsolidated structure 118 having a thickness T₅ and a cooling channel120, according to block 114. The second consolidated structure 118 mayhave a constant or variable cross section and may have a desired lengthL₁ and thickness T₅. It should be appreciated that the consolidatedstructure 118 may have more than one cooling channel 120. The coolingchannels may be equal, meaning each channel has the same dimensions, orthey may have variable dimensions, where each channel has differentdimensions, or a combination thereof.

Returning to FIG. 8, the method 100 also includes machining conductivechannels into the sealed consolidated structure to produce a coil (block122). For example, the machining performed in accordance with block 122may produce one or more desired coil geometries, such as curves, bends,varying angles and turning radii, and so on.

Before, during, or after forming the desired coil geometries, electricalconnectors, jumpers, and cooling fluid connectors may be deposited ontothe coil (block 124). For example, using ultrasonic consolidation, oneor more connector features may be consolidated to the existingstructure, obviating the use of solder, or other similar jointmechanisms.

As also noted above, in certain embodiments, in addition to, or in lieuof using ultrasonic consolidation, the gradient coils 26, 28, and 30 maybe deposited using laser powder deposition (LPD) or electron beammelting (EBM). To facilitate discussion of certain aspects of thesemethods, reference will be made to the structures in FIG. 9. In suchmethods, a focused laser/electron beam melts, sinters, or otherwiseconsolidates a portion of the bonding layer 74 such that the conductormaterial (e.g., in the form of a powder or wire) introduced at thejunction between the laser/electron beam and the surface of the bondinglayer 74 may be fused onto the surface of the bonding layer 74.Subsequent layers of conductor material are deposited in a similarmanner; that is, each layer of the conductor material is fused to adesired portion of the preceding layer to produce a consolidatedstructure similar to the middle structure seen in FIG. 9. Coolingchannels may be incorporated into the consolidated structure by advancedtool path planning or introducing a sacrificial material such as, butnot limited to, a fluid (e.g., water), fugitive ink, polymer, and/ormetal with low melting point into the cavity 112 prior to deposition ofadditional layers of the conductive material that seal the cavity 112 toproduce the consolidated structure 118. The sacrificial material may beremoved via physical and/or chemical processes (e.g., dissolution,flushing, ejecting, etc.) from the consolidated structure 118 resultingin the cooling channel 120. In yet further embodiments, the cavity 112may be formed by etching the first consolidated structure 108 using thelaser/electron beam.

The gradient coils 26, 28, and 30 produced from the methods andtechniques described above may have relatively simple geometries (e.g.,substantially straight or having relatively simple bends or turns) ormore complex geometries (e.g., a plurality of turns having differentdirections or geometries). For example, in one embodiment, the gradientcoils 26, 28, and 30 may have a round cross-sectional geometry.Moreover, as discussed above, the geometry of the cooling channels maybe equal or may have variable dimensions, or a combination thereof.Furthermore, the cooling channels may diverge or converge at a turnspacing of the gradient coil assembly 86 so as to enable a desired flowof a cooling fluid through the channels and suitable contact between thecooling fluid and the surface of the gradient coils 26, 28, and 30.

As noted above, the embodiments described herein enable themanufacturing of gradient coil assemblies used in MRI systems usingadditive manufacturing techniques. One system capable of suchmanufacturing is depicted in FIG. 10. In particular, FIG. 10 is anembodiment of an additive manufacturing system 130 that performs themethods of FIGS. 2 and 8. The additive manufacturing system 130 includesan additive manufacturing apparatus 132, a consolidation platform 134, amachining tool 136, and a system controller 138. The additivemanufacturing housing 132 further includes a feed mechanism 140, apositioning device 142, a metal deposition device 144, and a dielectricmaterial dispenser 150. The feed mechanism 140 is configured to supplythe positioning device 142, the metal deposition device 144, and/or thedielectric material dispenser 150 with materials used to build thegradient coil assembly, such as the gradient coil assembly 86 depictedin FIG. 7. For example, the feed mechanism 140 may supply anelectrically conductive material including, but not limited to, metalssuch as aluminum, copper and/or their alloys, electrically conductivecomposite materials, or a combination thereof, to build a consolidatedstructure to form an inductor. The conductive material may be in theform of a sheet, ribbon, tape, wire, powder, or any combination thereof.In other embodiments, the feed mechanism 140 may supply dielectricmaterials, such as ceramics and/or ceramic epoxies to the dielectricmaterial dispenser 150 to form a dielectric spacer layer (e.g.,dielectric spacer layer 82 of FIG. 7).

The positioning device 142, during operation, positions variousmaterials (e.g., coil material, dielectric spacer material, substratematerial) according to information received from the system controller138. For example, as discussed in further detail below, a coil designmay be input via a computer-assisted drawing program and provided to thesystem controller 138, which may in turn command operation of the system130 to construct the coil board/assembly according to the predefinedgeometric specifications. In particular, the system controller 138 maycommand the operation of the positioning device 142 to move certainfeatures of the additive manufacturing apparatus 132, such as the metaldeposition device 144 and/or the dielectric material dispenser 150.

In constructing the gradient coils, for instance, the positioning device142 may move the metal deposition device 144 (e.g., an ultrasonicconsolidation head, a laser, or an electron beam emission device) to apoint on a base layer, such as the base layer 68 in FIG. 3, on themandrel 70 supported by the consolidation platform 134. The metaldeposition device 144 may deposit the conductive material, supplied bythe feed mechanism 140, onto the base layer 68. The metal depositiondevice 144 then consolidates the conductive material to, and, along withthe machining tool 136, forms the conductive and cooling channels of thegradient coils 26, 28, and 30. As set forth above, in one embodiment,the metal deposition device 144 is an ultrasonic consolidator. Theultrasonic consolidator applies force (e.g., approximately 1000-3000 N)and ultrasonic vibrations (e.g., frequency approximately 20 kHz,amplitude between 10 and 50 μm) to the conductive material toconsolidate each layer of the conductive material and form the inductor,such as the consolidated structure 118 depicted in FIG. 9. In otherembodiments, the metal deposition device 144 includes a laser emitter orelectron beam emitter that melts, sinters, brazes, fuses, or otherwiseconsolidates each layer of the electrically conductive material to yieldthe consolidated structure 118 depicted in FIG. 9.

In constructing the coil assemblies, the positioning device 142 may movein concert with the mandrel 70, which may be coupled to a motor 154. Thesystem controller 138 may control the mandrel 70 to cause the mandrel 70to rotate and translate on the consolidation platform 134, therebyenabling construction of the inductor and cooling channels on a gradientcoil board (e.g., gradient board 66 in FIG. 5). Again, the machiningtool 136, working in concert with the metal deposition device 144, maymachine desired inductor and cooling channel patterns into theconsolidated conductive materials. For example, when the metaldeposition device 144 consolidates the conductive material, themachining tool 136 may machine the inductor and/or cooling channelpatterns according to information received from the system controller138.

As discussed above with respect to the method 60 of FIG. 2, uponcompletion of the inductor and cooling channels, the dielectric materialdispenser 150 deposits the dielectric spacer layer 82. The dielectricmaterial dispenser 150 receives a dielectric material, such as but notlimited to, ceramic, ceramic/epoxy composites, or any other suitabledielectric material, from the feed mechanism 140. The dielectricmaterial dispenser 150 may deposit the dielectric material onto thegradient board using a spray mechanism, or any other suitable dielectricdeposition mechanism.

As noted above, predetermined geometries for the various layers of thegradient coil assemblies may be input to the system controller 138,which enables the system controller 138 to in turn command the operationof various features of the additive manufacturing apparatus 132 toconstruct the desired gradient coil assembly. Accordingly, the additivemanufacturing system 130 may also include features that enable a user tointerface with the system controller 138 and other devices of the system130. For example, the system controller 138 may include devicesemploying a general purpose or an application-specific computer, both ofwhich may include memory circuitry for storing gradient coil parameterssuch as inductor, cooling channel, connector geometries and patterns,and images (e.g., of a desired conductor configuration). The systemcontroller 138 also may include a computer numerical controller (CNC)for the automated manufacturing of gradient coil boards. The CNC mayenable enhanced accuracy, automation, and repeatable construction ofinductor and cooling channels (e.g., the same type of inductor and/orcooling channel can be made each time) compared to more traditionalconstruction methods such as hand winding, which in turn improvesquality control and the overall efficacy of the gradient boards.

The system controller 138 may include a wide range of devices forfacilitating interface between an operator and the additivemanufacturing system 130. In the illustrated embodiment, for example,the devices include a monitor 160, a conventional computer keyboard 162,and an alternative input device such as a mouse 164. For example, thesystem controller 138 may include a computer assisted drawing ormodeling program enabling a user to define various coil and layergeometries. A printer 166 may be used to generate hard copy outputs ofinductor, cooling channel, and/or connector parameters, geometries, andimages of gradient coil board designs.

The system controller 138 may also receive information indicative of thequality of the inductor and cooling channels from an inline qualityinspection module 168. For example, the inline quality inspection module168 may provide information about the conductor, cooling channel, andconnector geometries to the control system 138, therefore the controlsystem 138 may compare the received information to specifications rangesstored in the memory circuitry and adjust the gradient coil parametersaccordingly. In certain embodiments, the metal deposition device 144 mayinclude integrated inspection sensors, such as optical charge-coupleddevices, for monitoring and verification of the additive manufacturingsteps. In certain embodiments, the quality inspection module 168 mayprovide feedback to the system controller 138 indicative of errors inconstruction. The controller 138 may use the feedback to adjust theoperation of one or more features of the additive manufacturingapparatus 132 to meet the predefined specifications for the variousgeometries (e.g., of the coils, cooling channels, spacer layers) inputinto the system 130.

This written description uses examples to disclose the invention,including the best mode, and also to enable any person skilled in theart to practice the invention, including making and using any devices orsystems and performing any incorporated methods. It should also beunderstood that the various examples disclosed herein may have featuresthat can be combined with those of other examples or embodimentsdisclosed herein. That is, the present examples are presented in such away as to simplify explanation but may also be combined one withanother. The patentable scope of the invention is defined by the claims,and may include other examples that occur to those skilled in the art.Such other examples are intended to be within the scope of the claims ifthey have structural elements that do not differ from the literallanguage of the claims, or if they include equivalent structuralelements with insubstantial differences from the literal languages ofthe claims.

What is claimed is:
 1. A method of manufacturing, comprising: producinga gradient coil assembly comprising one or more gradient coils for amagnetic resonance imaging system by a process, wherein the processcomprises: depositing a first layer comprising a base material onto asurface to form a substrate; depositing a second layer onto the firstlayer, wherein the second layer is configured to enable bonding betweena conductor material and the substrate; and depositing a third layeronto the second layer using a consolidation process, wherein theconsolidation process uses the conductor material to form at least aportion of an inductor.
 2. The method of claim 1, wherein depositing thefirst layer comprises: depositing the base material onto the surface,wherein the base material comprises a composite ceramic material; andcuring the composite ceramic material to form a base layer.
 3. Themethod of claim 1, wherein depositing the second layer comprisesspraying or soldering a radio frequency shielding material onto thesubstrate to form a bonding layer.
 4. The method of claim 1, wherein theconsolidation process forms the inductor as at least one of the one ormore gradient coils or a resistive shim coil.
 5. The method of claim 1,wherein the consolidation process comprises: depositing layers of theconductor material to form a consolidated structure; forming a coolingchannel in the consolidated structure; and depositing additional layersof the conductor material to form the inductor.
 6. The method of claim4, wherein the consolidation process uses ultrasound, a laser, anelectron beam, or a combination thereof, to form the consolidatedstructure.
 7. The method of claim 1, comprising depositing a spacer ontothe third layer, wherein the spacer is configured to isolate thegradient coil from one or more conductors used to provide current to thegradient coil.
 8. The method of claim 7, wherein the spacer comprises adielectric material.
 9. The method of claim 1, wherein the substrate iscylindrical.
 10. The method of claim 1, comprising depositing asacrificial material between the second layer and the third layer toform shim pockets.
 11. The method of claim 1, wherein the consolidationprocess forms an electrical connector, a coolant connector, or acombination thereof, coupled to the inductor without soldered or brazedjoints.